Well it doesn't specifically say anything in The Bible (if we're going by christianity) about masturbation. But its clear that God wanted to keep our relations pure. Plus, you had in the whole lust factor. We aren't supposed to look lustifuly at each other. Its not that you're going to burn in hell for masturbation, but I don't think God would approve of wanking it or whatever you want to call it.
And I guess masturbation is better than sexual intercourse. You only "corrupt" one person.